INHERITANCE BY PROTOTYPE : FIELD NOT RECONGNIZED

I'm working on stock.picking.out wich inherits by prototype from stock.picking, So , i want to add a field on

stock.picking.out, the inheritance by prototype says that every field added on stock.picking.out is not recognized by views, and that's what hapenning with me I guess.

Because I added a field num_bl on stock.picking.out (By custom module), and I overwrite a method ofstock.picking (force_assign), so I have now the following elements added to stock.picking.out, like this :

When running the force_assign overriden method, it shows following error Attribute error : Num_bl, it dosn't recognize the field num_bl, because of inheritance by prototype.

When I add the field num_bl manually ( direclty on source code without custom module) on stock_picking, it works, but it affects other databases, so I tried to add it on stock_picking with a custom module, but it shows only on the view_picking_form view, of stock_picking.

I am kind of confused, I'm looking for a solution that provides me adding the field on the stock_picking model (By custom module), exactly if I did it manually (direclty on the source code).